1. Field of the Invention
This invention relates to high density electronic packaging modules, and more particularly, to a three-dimensional multichip module comprised of memory and processor chips packaged in a single compact structure.
2. Description of the Related Art
To provide improved performance, manufacturers of integrated circuit chips continually strive to increase packaging density, which has led to the development of high density electronic packaging modules such as three-dimensional multichip structures. These multichip structures typically include a plurality of semiconductor chips that are adhered together in a stack so as to reduce the amount of space the chips occupy inside a system. It is generally understood that each chip in the stack has conductive leads that extend to one edge of the chip to provide electrical contact with external circuitry. Typically, a metallization pattern is provided on one side of the stack to establish electrical connection to circuitry external to the stack.
Disadvantageously, these multichip structures may not be suitable for IC chips that generate excessive heat during operation because it is difficult for heat to dissipate when the chips are sandwiched in a stack with other chips. Moreover, chips that generate excessive heat can transfer heat to adjacent chips in the stack and cause the adjacent chips to also overheat. Furthermore, the conventional multichip structures have limited space available on the side of the structure for interconnection wiring. As such, these structures may also not be suitable for chips that require numerous electrical connections to other chips in the same stack.
Thus, most conventional multichip modules are typically comprised of chips that perform essentially the same function because “same function” chips generally do not require extensive interconnection with each other. For instance, the memory chips of a system are often incorporated into multichip structures because memory chips do not have to be extensively interconnected with each other. Furthermore, memory chips also tend not to generate excessive heat and are thus suitable for stack configuration.
Conversely, non-memory chips such as processor chips, logic chips, and A to D converter chips are usually not included as part of a multichip module because these chips generate higher heat per unit area and can be difficult to cool when sandwiched in a stack with other chips. In addition to cooling problems, processor chips, in particular, often require extensive interconnection with other chips in the module. In some instances, there is insufficient space on the multichip structure to accommodate all the necessary conductive leads required to interconnect the processor chips to various other chips in the module. Although through chip connections have been proposed to make inter-chip connections, see for example, U.S. Pat. No. 5,270,261, the process of forming these connections adds to the cost and complexity of fabrication. In light of the foregoing disadvantages, processor chips and many other non-memory chips are typically not incorporated in conventional multichip modules.
However, as computerized instruments continue to decrease in size, it becomes more desirable to combine chips of an entire system, including memory, processor and logic chips into one compact structure. Hence, it will be appreciated that there is a need for a multichip structure that comprises chips of an entire system and can be installed into and removed from the system as a unit. To this end, there is a particular need for a multichip structure that combines memory and non-memory chips in the same structure in a manner such that these chips are conveniently interconnected with each other and there is adequate cooling for chips that generate large heat per unit area.